Bulk-solidifying amorphous alloys have been made in a variety of metal systems. They are generally prepared by quenching from above the melting temperature to the ambient temperature. Generally, high cooling rates on the order of 105° C./sec, are needed to achieve an amorphous structure. The lowest rate by which a bulk solidifying alloy can be cooled to avoid crystallization, thereby achieving and maintaining the amorphous structure during cooling, is referred to as the “critical cooling rate” for the alloy. In order to achieve a cooling rate higher than the critical cooling rate, heat has to be extracted from the sample. Thus, the thickness of articles made from amorphous alloys often becomes a limiting dimension, which is generally referred to as the “critical (casting) thickness.” A critical casting thickness can be obtained by heat-flow calculations, taking into account the critical cooling rate.
Until the early nineties, the processability of amorphous alloys was quite limited, and amorphous alloys were readily available only in powder form or in very thin foils or strips with a critical casting thickness of less than 100 micrometers. A new class of amorphous alloys based mostly on Zr and Ti alloy systems was developed in the nineties, and since then more amorphous alloy systems based on different elements have been developed. These families of alloys have much lower critical cooling rates of less than 103° C./sec, and thus these articles have much larger critical casting thicknesses than their previous counterparts. The bulk-solidifying amorphous alloys are capable of being shaped into a variety of forms, thereby providing a unique advantage in preparing intricately designed parts.
The use of hard materials in the formation of intricately designed parts for a variety of uses significantly improves the life of the article, but also imposes difficulties in its manufacture and assembly. Many parts of articles, such as electronic devices, machine parts, engines, pump impellers, rotors, and the like, must be assembled and connected to one another. Other objects or articles sometimes require the connection to be a pivotal connection, enabling movement of the respective parts. Most of the conventional pivotal connections, which are common in many orthopedic applications, are made after the parts have been molded, machined, or otherwise fabricated. These pivotal connections, or movable joints, suffer insofar as they sometimes become dislodged from one another, which for orthopedic applications (such shoulders, hips, and knees), such dislocation may be extremely painful. In other applications, dislocation of the movable parts may cause the device to malfunction or be completely destroyed.
It would be desirable to provide a connection or joint between parts that can move with respect to one another, and that will not become dislodged during use. It also would be desirable to provide a connection between extremely hard parts that are difficult to precision machine after molding.